This application seeks partial support for a Gordon Research Conference on the Population Biology and Evolution of Microorganisms. This will be the fifth such conference, which has been held biennially since its first meeting in 1985. The conference brings together scientists working in molecular genetics, population biology, microbiology and infectious disease, all of whose disciplines interact to define the main topic of this conference. There are virtually no conferences that assemble this blend of expertise. A detailed description of the aims of the conference, its significance and the plans for the next meeting are attached.